I lived on the East Coast as a child. One summer day when I was 12, I was on an outing with a church youth group at the seaside home of one of the church's leaders. He had a motorboat, and offered to teach anyone interested to water ski.

I watched in silence as every other kid called home and got permission.

The youth group leader couldn't understand why I hadn't asked to borrow the phone.

"Don't you want to come?"

"Yes," I said, desperately wanting to learn to water ski, knowing that I'd probably never have another chance. "But my mother will never agree."

"You'll never know if you don't phone. You might be surprised."

I rolled my eyes at his optimism, but reluctantly agreed to ask.

"No," my mother said.

"Everyone else's parents said yes."

"That's irrelevant, and you know it."

"This is a church leader, not some random careless stranger."

"No, you are not to go in the water or on the boat."

"What are the odds I'll get hurt? One-tenth of one percent?"

My mother brought out the big guns, her final word in every argument about risks:

"If it happens to you, it's 100 percent."

You may chuckle or you may groan. But the chances are that your mental math works much the way my mother's did -- at least when it comes to your health care. That is, you may seek testing or treatment when the odds are very small that such health care will actually help you -- because if it does work for you, then as far as you're concerned, it works 100 percent of the time.

Consider the facts reported in a New York Times article about prostate cancer screening via the PSA test. One life may be saved for every 1,000 men screened. However, 43 men out of every 1,000 screened will face "serious harms" from the resulting treatment. These harms range from incontinence to heart attacks. And one of every 3,000 men tested will die of complications of treatment they got because of this test.

The U.S. Preventive Services Task Force recommended against PSA testing for healthy men with no symptoms. But this recommendation met with the medical community's equivalent of howls of protest.

The argument goes, in effect, "Maybe you'll be the one in a thousand. Maybe you'll be the one whose life could be saved by screening." As my mother would have added, "If that happens to you, it's 100 percent."

Curiously, though, most people don't seem to ask, "What if you're one of the 43 out of 1,000 harmed as a result of treatment that is given because of screening?"

Our attitude seems to be, "If I don't take action, and it turns out that I have a big problem or it turns out that I will die because I didn't take action, I'll never forgive myself. But if I take action and the care I get causes a big problem, well, there's nothing I can do about it. I did what I could do. What happens next is out of my hands."

Consider what happens near the end of life. Most people will say that they don't want aggressive medical treatment for themselves if they are dying. But they have trouble sticking with this concept when the situation concerns family members or other loved ones -- even when it is known that the chances that the treatment will help are vanishingly small.

This approach might be called the "we don't stop until we run out of treatments -- and we never run out of treatments" approach. It is reflected in the words of the CEO of a hospital in Los Angeles, quoted in a New York Times article: "If you come into this hospital, we're not going to let you die."

This stance defies logic -- everyone will die eventually. But it offers comfort -- there's always something to be done, and maybe one of those tests or treatments will give you back your life. Even if the odds are very long, "If it happens to you, it's 100 percent."

With all due respect to my mother, it might be useful if we all started to rethink that math.